The invention relates to a motor vehicle having at least one control device, having an electronic power unit and having an energy storage system. The energy storage system includes a first electric energy storage device and a second electric energy storage device which is connected in parallel, or can be connected in parallel, with the first electric energy storage device.
Owing to the number of electric loads in modern motor vehicles, the need to ensure the electrical supply during the development of the vehicle has recently been subjected to novel requirements. This leads to a situation in which relatively complex on-board power system architectures are proposed in order to be able to cover energy requirements in the vehicle. This is mentioned, for example, in DE 10 2009 008 177 A1.
In addition, the relatively complex on-board power system architectures, in particular on-board power system architectures of hybrid vehicles with a partially electrified drive train, require a complex energy management system in order to regulate energy flows in the vehicle in a targeted fashion. This is disclosed, for example, in US 2005/0228553 A1, in which a partially predictive energy management system for hybrid vehicles is described.
An object of the invention is to provide an improved motor vehicle having a control unit, having an electronic power unit and having an energy storage device. The energy storage system includes a first electric energy storage device and a second electric energy storage device which is connected in parallel, or can be connected in parallel, with the first electric energy storage device.
This and other objects are achieved by a motor vehicle having a control device, having an electronic power unit and having an energy storage system which comprises a first electric energy storage device and a second electric energy storage device which is connected in parallel, or can be connected in parallel, with the first electric energy storage device. According to the invention, the two energy storage devices have a common base voltage at respectively different states of charge. The base voltage is substantially adjustable by the electronic power unit. A predictive energy management system that can be executed on the control device determines a predefined setpoint value of the base voltage as a function of a predicted charge balance of the energy storage device.
This means that a base voltage which deviates from the common base voltage can be adjusted by the energy management system of the vehicle. The actual setting of the voltage is carried out by the electronic power unit, such as for example by a DC-DC converter, a generator or implicitly by a negative over-potential at the energy storage devices forming the energy storage device, as a result of a discharge current for supplying electric loads. The predefining of the base voltage by the energy management system is carried out in such a way that specific advantages of the energy storage devices forming the energy storage device are exploited in the imminent use profile of the vehicle.
According to one preferred embodiment of the invention, this is done in that the predictive energy management system increases the base voltage when there is an imminent use profile of the vehicle which gives rise to a predicted negative charge balance.
When a negative charge balance is present and when a negative charge balance is imminent, the base voltage is increased. The base voltage is therefore increased owing to the predicted negative charge balance even when there is a use profile which constitutes a well-balanced charge balance of the energy storage device at a particular time. In this way, the cycling of the energy storage devices can be shifted predictively in favor of reduced cycling of the one energy storage device and increased cyclic use of the other energy storage device. This is advantageous when an energy storage device with particularly fixed cycles is used. The energy storage device which has fixed cycles is preferably the energy storage device with the relatively low relative state of charge at a given coupling voltage, with the result that said energy storage device is operated below the increased cycle load.
In addition, the predictive energy management system increases the base voltage when there is an imminent stationary phase. As a result, the degree of cycling of the energy storage device is additionally shifted in the direction of the energy storage device with fixed cycles.
Furthermore it is advantageous if the predictive energy management system reduces the base voltage when there is an imminent use profile of the vehicle which gives rise to a predicted positive charge balance.
The base voltage of the energy storage device can be lowered if the imminent use profile of the vehicle indicates a positive charge balance. In this way, in particular, the recuperation potential in the case of a vehicle with a braking energy recovery function (BER), which is known to a person skilled in the art, is maintained. This increases the efficiency during the recovery of braking energy by way of a charge current which is increased owing to a lower state of charge and a higher over-potential when the recuperation voltage is applied.
The predictive energy management system determines, for an imminent time period, the charge balance of the energy storage device on the basis of a selection and/or a combination of the following data sources: navigation data, traffic information data, route-related weather data, detection data of a type of vehicle user, vehicle-to-vehicle communication data, route-frequency-detection data, status data of the electronic power unit and status data of the two electric energy storage devices such as the state of charge or temperature.
The energy management system, which can run as software on one or more vehicle control devices, has a plurality of information inputs of sensors of the vehicle, of actuators of the vehicle and of communication interfaces of the vehicle. On the basis of a current information situation, the energy management system determines a prediction of the charge balance of the energy storage device for a specific imminent period of use of the vehicle. The energy management system can also include self-learning algorithms. The predefining of the base voltage is carried out within defined limits which are characteristic of the electro-chemical properties of the energy storage device. In this context, the predefining of the base voltage in a first approximation is inversely proportional to the determined charge balance.
Possible sensors which are available to the vehicle are, in particular, battery sensors which are assigned to the respective energy storage devices and which record the voltage, current and temperature of the respective stores as a function of time.
The energy storage device can be implemented, for example, if the first energy storage device is embodied as a lead acid battery and the second energy storage device as a lithium-ion battery.
These two energy storage devices are advantageously characterized by partially overlapping open-circuit voltage characteristic curves, wherein the lead acid battery has a significantly lower discharge internal resistance at high current rates over all the relative states of charge than the lithium ion battery, and the lithium ion battery has a significantly lower charge internal resistance than the lead acid battery over all the relative states of charge.
The invention is based on the considerations presented below.
The starting point is a conventional vehicle on-board power system with an individual lead acid battery as an energy storage device for the basic on-board power system, wherein the vehicle is equipped, if appropriate, with micro-hybrid functionalities such as a braking energy recovery function and/or with an automatic engine stop/start system (MSA).
Operating strategies for the conventional on-board power system can include maximizing the service life of the lead acid battery (LAB). This can be achieved with the LAB technology known to a person skilled in the art, in particular in the case of permanent full charging of the LAB, i.e. when a full charging strategy is used. However, in order to provide the possibility of recuperation of electrical energy converted from kinetic energy even with the LAB, a selectively partially discharging operating mode of the LAB is selected, which mode can have a disadvantageous effect on the service life of the LAB. This can be particularly disadvantageous in unfavorable operating states if the state of charge of the LAB is additionally lowered by frequent stop phases by the MSA and by excessive discharging in the parking and running on phase of the vehicle.
Modern 2-battery concepts dispose of energy storage devices comprising different chemical technologies such as, for example, the combination of a lead acid battery (LAB) with a lithium ion battery (LiB).
In the case of energy storage devices which are connected in parallel in a voltage-neutral fashion, i.e. in the case of direct galvanic connection, a common voltage occurs at the energy storage devices, which voltage is referred to as a coupling voltage (common base voltage).
For a vehicle with such an energy storage device, an adept energy management system is proposed which makes predictive use of the specific respective advantages of the LAB and of the LiB specifically in the context of the energy storage device, i.e. in the presence of the respective other energy storage device.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.